The present invention relates to a hermetic motor compressor unit, particularly to such a unit which is intended for use in small capacity applications, such as small refrigerators.
One of the primary concerns in designing refrigeration compressors for use in small capacity applications is that of minimizing the overall size of the unit without sacrificing efficiency or the capacity which is required. A further design consideration is that of minimizing the number of parts required and the assembly time. This is particularly important in small compressors because the manufacturing volume of such compressors is normally quite high and even small savings in material and labor reaches considerable proportions when high production levels are attained.
In hermetic compressors, the motor-crankcase assembly is generally resiliently supported within the outer housing by means of spring supports. This not only isolates vibration and noise generated by the compressor, but provides some degree of isolation between the motor-crankcase assembly and shocks imparted to the housing during shipping and use.
One prior art mounting arrangement comprises a plurality of mounting spuds pressed over the heads of the screws or bolts extending through the stator laminations and resiliently retained within a plurality of respective coil springs secured to the lower surface of the outer housing. The springs are mounted to the housing by means of metal mounting spuds welded or brazed to the housing and extending axially within the coil springs. In addition to serving as the connectors to the coil springs, the spuds serve as shipping stops to limit the vertical movement of the motor-crankcase assembly within the housing.
Generally, the sockets in the upper spuds that are pressed over the heads of the connecting bolts or screws are concentric with the central axis of the spud. Because the connecting bolts or screws are necessarily disposed inwardly of the sides of the stator laminations to provide the required degree of structural integrity between the bolts and laminations, the support base for the assembly, as defined by the four support spuds, is also disposed inwardly of the sides of the laminations to the same extent. If the geometrical centers of the spuds could be relocated outwardly, then a more stable support base for the motor-crankcase assembly could be provided.
The mounting spuds and their associated coil springs present a problem in that they often interfere with the end turns of the field windings, which extend out of the slots of the stator and form a mass on the lower surface thereof. This necessitates that the end turn configuration for the field winding be carefully controlled so that the end turns do not come into contact with the springs, which may result in wearing through of the insulation and shorting of the winding.
Generally, compressors of this type are designed such that there will be no contact between the motor-crankcase assembly resiliently supported within the housing and the inner wall of the housing during normal use. During shipping of the unit, however, it is often subjected to severe shocks thereby causing the motor-crankcase assembly to strike the inner wall of the housing and cause damage to the compressor or rupturing of the hermetically sealed housing. Undue movement of the motor-crankcase assembly is also necessary to prevent overstressing of the mounting springs and discharge gas shock loop.